The intracranial pressure of a mammal subject results from a complex sum of pressures and volume changes within the central nervous system of the subject. The skull generally protects the central nervous system from external deforming forces. In a child with an open fontanelle ("soft spot" on the head of an infant), the cranial vault is likely to be deformed leading to increased intracranial pressure or displacement of brain tissue. When a tight head dressing is applied, venous blood frequently does not freely flow into the scalp with a resultant increase in intracranial pressure. Intracranial volume changes can result from increases in the cerebrovascular blood volume, intracranial bleeding, infections, cerebritis, abscesses or empyemas, increases in brain tissue such as central nervous system tumors and disequilibrium between the cerebrospinal fluid production and absorption. Changes in intra-abdominal pressure, as caused by e.g. coughing and sneezing, can be transmitted by the epidural venous plexus to the intracranial cerebrospinal fluid (CSF) compartment. Respiratory variations due to inhaling and exhaling can affect venous return to the heart and cardiac pulsations can result in pressure and volume changes in the cerebrovascular system.
Because the CSF is compartmentalized, an increase in pressure in one compartment can result in CSF flowing into an adjacent compartment, i.e. a circulation of CSF. Choroid plexus pulsations can promote flow out of the ventricular system and venous epidural pulsations move CSF out of the intraspinal compartment. Brain expansion from increases in cerebrovascular blood volume helps CSF flow out of cisterns containing fluid sacs. When treating diseases affecting intracranial pressure it is important to try to re-establish CSF circulation and to normalize the intracranial pressure. In an attempt to resolve these problems, brain ventricle to peritoneum shunts have been developed to supply CSF from the brain to the peritoneum of the subject.
A problem with prior art ventricle to peritoneum shunts is that they do not restore the CSF circulation lumbar shunt must initially have excessive tubing; otherwise the shunt must be removed and replaced from time to time. A solution is to insert a large loop of excessive tubing into the peritoneal cavity. The tubing is pulled outward as the subject grows both in height and circumferentially.
Subjects with syringomyelia and craniocerival junction abnormalities, including the Chiari malformations, may be amenable to a bypass. Syringomyelia is associated with a change in the CSF accumulator function. When fluid pulse waves cannot be easily transferred up and down the spine, the spinal cord is subjected to "shock waves." Ordinarily, fluid pressure changes cause the CSF to flow parallel to the spinal cord so the resulting force vector is parallel to the spinal cord axis. When there is an obstruction to CSF flow and CSF cannot be displaced into another compartment, the fluid pulse waves cause a temporary pressure elevation in the obstructed compartments. If the force vector of the fluid pulse waves is not parallel to the spinal cord but angled towards the perpendicular, the force is transmitted into the spinal cord. The spinal cord portion having the lowest resistance to the force vector is thereby subjected to the shock waves and can become a pathological site for CSF accumulation. The resistance is lowest at the softest spinal cord sites or those having the highest water content. Hence, gray matter has a lower resistance than white matter and softened spinal cord from ischemic changes or traumatic changes is more subject to syrinx formation.
CSF flows into the spinal cord when the shock wave pressure exceeds the resistance of a portion of the spinal cord. If the pressure outside the spinal cord is significantly greater than the pressure inside the cord and the resulting pressure differential is greater than the force vector resistance, CSF can flow in towards the although they provide a decrease in intracranial pressure. When a subject has a raised intracranial pressure associated with a block in CSF circulation, the present treatment of choice is to surgically relieve the obstruction, either by removing the obstructing lesion or creating a communication between an obstructed compartment and the open CSF circulation. An example of the former is removal of a posterior fossa tumor to alleviate a fourth ventricular obstruction. An example of the latter is forming a third ventriculostomy in a subject with a benign tectal glimoa leading to aqueductal obstruction.
When neither of these alternatives is feasible an attempt may be made to bypass the obstruction by inserting a shunt from the obstructed compartment to the open CSF circulation. An example is a patient with a nonresectable hypothalamic optic pathway glioma causing an obstruction at the level of the third ventricle. In this situation the two lateral ventricles are coupled together by surgically opening the septumpellucidum. A ventricular catheter with proximal and distal holes is connected with distal tubing going into the lumbar thecal sac to drain both lateral ventricles. The resulting overdrainage into the lumbar thecal cavity restores the CSF circulation and there is no siphoning effect to be offset as with a brain ventricle peritoneum shunt. The lumbar sac is chosen because it does not interfere with the spinal cord, which at higher spinal levels could be traumatized by insertion of a shunt. A shunt going from the ventricular to the cisterna magna or subarachnoid space is also a possibility. Insertion of a shunt to the subarachnoid space over the convexity of the brain requires a craniotomy and an alternative material to the standard silicone elastomer. Silicone elastomers can lead to very thin membranes and loculation of the CSF in the subarachnoid space. However, in a growing child a cord. When the pressure outside the spinal cord lessens and is not significantly less than the cavitary pressure, the pressure might not be able to overcome the resistance of the spinal cord so CSF may not flow out of the syrinx into the subarachnoid space. Thus, transient pulsations in the intrathecal sac can lead to a "pumping up" of a syrinx within the spinal cord until the pressure within and outside the cord are equal. This accumulation tends to be greatest at regions where the force vector is most angled inward towards the curve, such as the normal cervical lordosis or in regions adjacent a kyphoscoliotic curvature. The accumulation tends to be greatest in the regions of the spinal cord where there is the most gray matter or the cord is softened due to some other pathological process, such as being compressed against the spinal canal in a kyphoscoliosis. This theory is consistent with having a syrinx formation at the C5-6 level in association with a Chiari malformation and small syrinx formation associated with scoliotic curvatures. This also explains the formation of syrinxes in the lumbar enlargement where there is more gray matter in subjects with tethered cords.
Inserting a syringosubarachnoid shunt lowers the resistance to flow between the syrinx cavity and subarachnoid space, thus allowing the syrinx to be more easily deflated when intraspinal subarachnoid pressures are lowered. In scoliosis, the cord is stretched over the concave portion of the spinal column curve, leading to softening of the curve and a lower resistance for CSF entrance. Since the CSF does not travel in a straight path, a shock wave pounds against the spinal cord just proximal to the curve and a syrinx can develop.
For a subject having a Chiari malformation, the shock wave strikes the spinal cord at the area of the greatest cervical lordosis. Thence, the resistance to the force vector from the shock wave is lowest in the portion of the cord with the greatest proportion of gray matter. Consequently, the syrinx often begins at the C5-6 level. The initial treatment for a syrinx with an obstruction at the craniocervical junction is to remove the odontoid process transorally if there is a ventral impingement. Such removal attempts to alleviate the obstruction and re-establish flow.
A posterior compression with duraplasty for a tight posterior fossa is an alternative treatment. The duraplasty can act as a pseudo meningocele reservoir and function as an accumulator. Despite a posterior fossa decompression and opening of the dura, the subject sometimes later develops an arachnoiditis. This can be near the suture line of the dural patch. This arachnoiditis can restrict the free flow of CSF, causing the subject to redevelop the syrinx.
In an effort to try to keep a pathway open, a stent can be inserted; however, the stent also can become obstructed, especially if there is already a stimulus for scar formation. Placing a stent from the syrinx to the subarachnoid space helps to equalize the pressure but is also prone to obstruction in the long run. Draining the syrinx to lower the pressure helps it to collapse even further so a syrinx to pleural or peritoneal shunt can be successful.
Another alternative is to provide a lower resistance pathway for CSF to return to the open CSF circulation such as with a shunt from the spinal subarachnoid space to the fourth ventricle or lateral cisterns. A problem with this approach is that sometimes the proximal end of the shunt irritates one of the cranial nerves in the lateral cisterns, causing the subject to have headaches, neck pain or other cranial nerve dysfunctions. If the shunt is on the floor of the fourth ventricle, it may irritate this area, with the patient experiencing postoperative nausea and vomiting. Shunting from the intraspinal subarachnoid space to the lateral ventricles might be less irritating and does not require a posterior fossa exposure. Placement of such a shunt is technically straightforward and a catheter can be placed percutaneously into the lumbar dural sac, tunneled up to the head and then placed into the lateral ventricle by way of a bur hole. An expandable reservoir can be interposed to act as an accumulator.
Another approach is to tunnel an intraspinal catheter up to the vertex of the head with distensible tubing interposed. At the vertex, the intraspinal catheter can be attached to an anti-siphon or siphon control device and then tunneled down to a distal cavity such as the pleura or peritoneum. This prevents overdrainage of CSF but allows easy escape of CSF if there is a positive pressure. Scarring around the antisiphon device alters coupling of atmospheric pressure to the CSF, leading to a malfunction of the shunt system. In subjects having external hydrocephalus from either a meningitis or subarachnoid hemorrhage, the obstruction cannot be bypassed to provide CSF reabsorption. In these situations the CSF is either diverted directly into the venous sinus or into another body cavity for absorption. A prior art brain ventricle to peritoneum shunt does not have accumulator capabilities, causing CSF circulation to remain abnormal, although it can control intracranial pressure (ICP). Thus, whenever CSF circulation receives a positive fluid pulse pressure, CSF exits by way of the shunt but when a negative fluid pulse pressure follows, CSF does not return to the CSF circulation. Until the lost CSF is produced, this negative pressure results in an increase in either the brain volume or intracranial blood volume. Thus the pulsatile intracranial pressure results in a gradual progressive emptying of the CSF compartments.
A possible solution to the problem of the CSF compartments gradually emptying through the use of prior art shunts is to attach the ventricular catheter to a three-way connector. From this connector, (a) one valveless tube is connected to the intraspinal subarachnoid space and (b) another tube having a valve goes to the distal body cavity. With this arrangement, the spinal subarachnoid space assumes an accumulator function. The resistance for CSF flow to the intraspinal compartment would be much less than the added resistance offered by the valve. However, there are several problems with this arrangement. First, it is a relatively complicated setup. Second, when the subject stands erect there must be an anti-siphon device proximal the distal cavity to prevent overdrainage or a flow control device must be inserted. Third, the intraspinal subarachnoid space is often involved in the disease process and cannot provide free circulation of CSF and therefore is severely limited in its accumulator function.
It is accordingly an object of the present invention to provide a new and improved shunt for regulating the flow of cerebrospinal fluid from the brain ventricles to the peritoneum of a subject to overcome the aforementioned problems.
Another object of the invention is to provide such a shunt for regulating CSF flow relatively independently of whether the subject is upright or lying down.
An additional object is to provide such a shunt wherein CSF flow is regulated somewhat independently of pressure pulses within the subject, due e.g. to coughing or sneezing.
A further object is to provide such a shunt that is relatively easy to remove from a subject to accommodate changes in the size of the subject, due, e.g. to growth of a child.
An added object is to provide such a shunt with a brain ventricle catheter having plural openings in a proximal end thereof, which openings are arranged to prevent occlusion of CSF within the catheter.
A further object is to provide such a shunt with a brain ventricle catheter having a structure and plural openings arranged so tissue cannot grow from openings on opposite side wall portions of the catheter.
An additional object of the invention is to provide such a shunt with a pressure responsive deformable outer wall for coupling pressure variations from within a subject to CSF flowing from the brain to the peritoneum.
Yet a further object is to provide a catheter with a pressure responsive deformable outer wall for coupling pressure variations from within a subject to fluid within the catheter, wherein the catheter includes internal structure for inhibiting collapsing and/or kinking thereof.
Yet another object of the invention is to provide a new and improved catheter having a structure and plural openings in a proximal end thereof, which openings are arranged to prevent occlusion of fluid within the catheter.